1. Field of the Invention
The invention relates to a magneto resistive effect head for reading a record from a recording medium by using the magneto-resistive effect.
2. Description of the Prior Art
Usually, a magnetic head provided in a hard disk drive (HDD) includes: a writing head for writing information as a magnetization signal onto a recording medium (hard disk); and a reproducing head for reading the signal recorded as a magnetization signal on the recording medium. Since the reproducing head is constructed by a stack including a plurality of magnetic thin films and non-magnetic thin films and reads the signal by using the magneto-resistive effect, it is called a magneto-resistive effect head. There are a few kinds of stacking structures of the magneto-resistive effect head and they are classified into an AMR head, a GMR head, a TMR head, and the like in accordance with a principle of magneto-resistance which is used. An input magnetized field entered from the recording medium into the reproducing head is extracted as a voltage change by using an AMR (Anisotropy Magneto-Resistive effect), a GMR (Giant Magneto-Resistive effect), or a TMR (Tunneling Magneto-Resistive effect).
In the stack layer of the reproducing head, a magnetic layer whose magnetization is rotated by receiving the input field from the recording medium is called a free layer. To suppress various noises such as a Barkhausen noise and the like or to control an asymmetry output, it is important to convert the free layer into a single domain in a track width direction. If the free layer has a magnetic domain without being converted into the single domain, the free layer receives the input magnetized field from the recording medium, so that a domain wall movement occurs and becomes a cause of the noise.
As a method of the magnetic domain control for converting the free layer into the single domain, for example, as disclosed in JP-A-3-125311, there is a method whereby magnetic domain control layers including magnet layers are arranged at both ends of the free layer, and a magnetic field which is caused in the track width direction from the magnet layers is used. FIG. 8 shows a schematic diagram which is obtained when a magneto-resistive head subjected to the magnetic domain control by such a method is seen from an air bearing surface. A free layer 2 is formed via a spacer 3 over a soft magnetic layer (called a pinned layer) 4 and magnetization of the soft magnetic layer 4 has been fixed by an antiferromagnetic layer 5. A cap layer 1 is formed on the free layer 2. A width of free layer 2 is called a track width Twr. Both ends of the stack of the antiferromagnetic layer 5 are shaved from the cap layer 1 by ion milling or the like, so that a device has a trapezoidal shape when it is seen from the air bearing surface as shown in FIG. 8. A structure of the head of FIG. 8 is characterized in that magnetic domain control layers 7 including magnet layers are arranged to both ends of the device via seed layers 6. According to such a structure, a magnetization distribution of the free layer 2 is controlled by using a magnetic field which is developed from the magnetic domain control layers 7 and the free layer is converted into the single domain.
As another method of the magnetic domain control, for example, as shown in U.S. Pat. No. 4,663,685, there is a method whereby antiferromagnetic films are stacked on both ends of a free layer and an exchange coupling between the antiferromagnetic film and the free layer is used. FIG. 9 shows a schematic diagram which is obtained when a magneto-resistive effect head subjected to the magnetic domain control by such a method is seen from an air bearing surface. A structure of the head of FIG. 9 is characterized in that the free layer 2 is formed via the spacer 3 over the soft magnetic layer (called a pinned layer) 4 whose magnetization has been fixed by the antiferromagnetic layer 5, and antiferromagnetic films 12 are stacked at both ends of an upper portion of the free layer 2.
A magnetic domain control is performed by an exchange interaction which acts between the antiferromagnetic film 12 and free layer 2. The free layer 2 is formed so as to be wider than the width of track written on the recording medium and has a shape such that end regions are fixed. According to such a structure, therefore, a record is read by a portion Tw (of the free layer 2) between the antiferromagnetic films 12 (such a portion is called a sensing region). A lead layer 10 is stacked over the upper surface of the antiferromagnetic film 12 via a seed layer 11. It is not always necessary to form the seed layer 11.
As shown in JP-A-11-203634, there is also a method of stacking an antiferromagnetic layer having a uniform thickness onto the whole surface of a free layer, or the like. However, since a track width of the present head is very narrow, there is a fear that, if the whole surface of the free layer is fixed by a uniform magnetic field, sensitivity deteriorates and a magnetic domain control field of a track end portion where the magnetic domain control is particularly necessary is contrarily insufficient. As shown in JP-A-2001-84527, a method whereby a magnetic domain control layer is constructed by a stack layer of a layer of high coercivity and at least one of a ferromagnetic layer and an antiferromagnetic film has also been proposed.
Each of the above magnetic domain control structures has the following problems. According to the magnetic domain control system as shown in FIG. 8 such that the magnetic domain control layers comprising the magnet layers are arranged on both sides of the free layer, since a magnetic field which is developed at an interface where the magnetic domain control layer and the free layer are come into contact with each other is too strong, a region (dead region) where the magnetization of the free layer is hard to be rotated with respect to the medium field is caused. To reduce the dead region, it is sufficient to weaken a magnetic domain control force by simply thinning the thickness of magnet layer or by another method. In case of using such a method, however, since an inconvenience such that the Barkhausen noise or an output signal instability is contrarily caused, asymmetry of an output increases, or the like occurs, the magnetic domain control force of a certain extent is necessary.
When a recording density of the recording medium is large and the track width Twr which is defined by the width of free layer is wide, since a ratio of the dead region which occupies the track width Twr is small, such an influence does not cause a large problem. However, the track width Twr is decreasing more and more in accordance with a recent extreme increase in recording density. Therefore, the ratio of the dead region which occupies the track width Twr is increasing. Unless some countermeasures are taken, it is very difficult to assure enough sensitivity of the head without deteriorating characteristics of noises or the like.
As one of the countermeasures, a method whereby an interval between leads is set to be smaller than the interval of the track width Twr and the portion of the dead region of low sensitivity is not used for reading, thereby enabling a high reproduction output to be obtained has been proposed in, for example, JP-A-9-282618 or U.S. Pat. No. 5,739,990. However, according to such a method, there is a problem such that since a magnetic domain control force which is applied to the end portion of the free layer locating under the lead is weak, a side reading increases.
According to the magnetic domain control method as shown in FIG. 9 whereby the antiferromagnetic film is arranged, since the coupling field acts only on the portion where the antiferromagnetic film and the free layer are in contact with each other, the problem of the dead region as mentioned above does not occur. It is advantageous for realization of a narrow track. However, the exchange coupling field between the antiferromagnetic film and the free layer is weaker than that in case of using the magnet layers and it is insufficient as a magnetic domain control force.
When the apparatus such as an HDD or the like operates, although the magneto-resistive effect device generates heat, the exchange field of the antiferromagnetic film is deteriorated by the heat. Therefore, a problem such that the edge region of the free layer which ought to have been fixed also has sensitivity, the side reading occurs, the record on the adjacent track is read, and an error rate deteriorates occurs.
It is an object of the present invention to provide a magneto-resistive effect head capable of realizing large sensitivity and excellent side reading and noise characteristics.
According to the invention, in a magneto-resistive effect head, a magnetic domain control of a free layer is performed by using both of antiferromagnetic films and magnetic domain control layers including magnet layers. For example, the magnetic domain control is performed by arranging the magnetic domain control layers including magnet layers to both ends of a magneto-resistive effect device having a pair of antiferromagnetic films for performing the magnetic domain control of the free layer.
This structure differs from the structures of both of the foregoing prior arts. For example, in the method of JP-A-2001-84527 whereby the magnetic domain control layer is constructed by the stack of the layer of the high coercivity and at least one of the ferromagnetic layer and the antiferromagnetic film, the antiferromagnetic film is used for aligning the magnetization of the high coercivity layer in the track width direction and not used for the magnetic domain control of the free layer. Even if the high coercivity layer is used, since there is a problem of the dead region, the problem remains in case of realizing the narrow track. However, according to the construction of the invention, the problem of the dead region can be solved.
FIG. 2 shows a distribution in the track width direction of the magnetic domain control field which is applied to the free layer. In case of the magnetic domain control using only the magnet layer of case (1), a record is read out from the track width portion Twr. It will be understood that although a magnetic field in the center portion of the track width is small, the magnetic field increases as a position approaches the track end portion. There is a problem such that the sensitivity deteriorates remarkably in the track end portion.
According to the magnetic domain control using only the antiferromagnetic film of case (2), the record is read out from the sensing region Tw of the center portion of the free layer. It will be understood that a uniform magnetic domain control field is applied only to the portion on which the antiferromagnetic film is overlaid and no magnetic field is applied to the sensing region. Therefore, although the realization of high sensitivity of the device can be expected, since the exchange coupling field intensity of the antiferromagnetic film is smaller than that of the magnet layer, there is a problem such that the record is read out from the whole free layer including not only the sensing region but also the end portions. To solve those problems, therefore, a new magnetic domain control construction using the magnet layers and the antiferromagnetic films has been invented.
According to a magnetic domain control using both of the magnet layers and the antiferromagnetic films, a distribution of a magnetic domain control field as shown by a bold line of case (3) is obtained. According to this magnetic domain control, the record is read out from the sensing region Tw of center portion of the free layer. In the end portion of the free layer, since the magnetic domain control is performed by a sufficient large effective magnetic field obtained by adding the powerful magnetic domain control field of the magnet layer and the exchange coupling field of the antiferromagnetic film, the problems of the side reading, noise, and the like do not occur.
On the other hand, since the sensing region is far from the magnet layer, no dead region is caused. Since the antiferromagnetic film is effective only to the end portion, no influence is exercised on this portion. Thus, the magnetic field which is applied to the sensing region is sufficiently weak and a magneto-resistive effect head having high sensitivity can be realized. By optimizing a thickness and a saturation magnetic flux density of the magnetic domain control layer including the magnet layers and a width of antiferromagnetic layer, a magneto-resistive effect head which has high sensitivity even if a track width is narrowed and in which a noise and side reading do not occur can be realized.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.